Problem: Determine how many solutions exist for the system of equations. ${6x+y = -8}$ ${y = -6-6x}$
Answer: Convert both equations to slope-intercept form: ${6x+y = -8}$ $6x{-6x} + y = -8{-6x}$ $y = -8-6x$ ${y = -6x-8}$ ${y = -6-6x}$ ${y = -6x-6}$ Just by looking at both equations in slope-intercept form, what can you determine? ${y = -6x-8}$ ${y = -6x-6}$ Both equations have the same slope with different y-intercepts. This means the equations are parallel. ${1}$ ${2}$ ${3}$ ${4}$ ${5}$ ${6}$ ${7}$ ${8}$ ${9}$ ${\llap{-}2}$ ${\llap{-}3}$ ${\llap{-}4}$ ${\llap{-}5}$ ${\llap{-}6}$ ${\llap{-}7}$ ${\llap{-}8}$ ${\llap{-}9}$ ${1}$ ${2}$ ${3}$ ${4}$ ${5}$ ${6}$ ${7}$ ${8}$ ${9}$ ${\llap{-}2}$ ${\llap{-}3}$ ${\llap{-}4}$ ${\llap{-}5}$ ${\llap{-}6}$ ${\llap{-}7}$ ${\llap{-}8}$ ${\llap{-}9}$ Parallel lines never intersect, thus there are NO SOLUTIONS.